1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus and a multi charged particle beam writing method. More specifically, for example, the present invention relates to drift correction of multiple beams.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with electron beams.
In a variable shaping type (VSB) electron beam writing that uses a single electron beam for writing, the more the pattern shape is complicated, the more it becomes necessary to divide the pattern into fine shot figures, so that the writing time becomes long. In order to solve this problem, it could be thought to shorten the writing time by increasing a beam current density so as to compensate the increase in the number of shots. However, if this method is employed, since the influence of resist heating and the like becomes large, there is also a limit to this method.
Now, think of a writing apparatus using multiple beams (multi-beams). Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time in multiple writing, the throughput can be greatly increased. In a writing apparatus employing a multi-beam system, for example, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes arranged in a matrix, blanking control is performed for each of the multiple beams, and each unblocked beam irradiates a desired position on a target object or “sample”.
In the case of a conventional single beam writing apparatus, the number of shaping aperture opening portions for focusing a shot image (pattern) on the substrate used as a target object is one. By contrast, in the case of a multiple beam writing apparatus, a plurality of shaping aperture openings are needed. Consequently, the size of a shaping aperture plate is large. The blanker array for blanking-controlling each beam of multiple beams may be united with the shaping aperture plate. Therefore, the structure becomes complicated. Thus, since the shaping aperture portion is large and the structure is complicated, a multi charge particle beam writing apparatus is easily affected by adherent contamination and beam drift occurs easily compared with a single beam writing apparatus. For example, in the case of a single beam writing apparatus of a variable shaped beam system (VSB system), the position of a first shaping aperture image having passed the first shaping aperture can be adjusted on the second shaping aperture by a deflector. Therefore, the position accuracy of the first shaping aperture can be corrected. However, in the case of the multi-beam writing apparatus, since the beam shaping is performed once, the position of the shaping aperture opening greatly affects the position accuracy when written on a target object surface. Therefore, if beam drift occurs at the shaping section of multiple beams, the position accuracy of each beam is degraded. When beam drift occurs, in addition to that the position of each beam is displaced, another problem may be generated in that a beam in the “on” state is partially blocked by the blanking aperture, thereby changing the dose reaching the target object. Thus, it is important to perform measurement and correction of the drift at the shaping section of multiple beams.
Conventionally, in order to increase the position accuracy of multiple beams at the target object surface, there has been suggested a technique that a beam for measurement, namely a beam to be measured, is shaped and its middle image is detected near the target object surface to correct the beam position (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2008-521221). However, with this technique, it is difficult to measure the amount of drift at the shaping section of the multiple beams, and thus correction cannot be performed sufficiently.